ok, the League of Extraordinary Gentlemen just got waaaaaay cooler. Checking the website, there are bios on the characters. You want to know who is part of this group?

Captain Nemo"Agent" Sawyer (First name not mentioned but tales of adventuring on the Mississippi...take a guess)Dorian GrayDr. Jekyll/Mr. HydeAllan QuaterrmainMina Harker (she who helped Van Helsing against Dracula)

both are fairly well known literary characters (like the rest of the League), Dorian Gray is the subject of the Oscar Wilde book "The Picture of Dorian Gray" (theres a synopsis of sorts on the movie website) and Quatermain is a character conceived by H.R. Haggard. some quick google searching should help you out :)

Agent (Tom) Sawyer was of course created by Mark TwainNina Harker by Bram StokerI'm assuming the Invisible Man is at least borrowed from H.G. WellsDr. Jekyll and Mr. Hyde by Robert Louis StevensonCaptain Nemo by Jules Verne